1. Field of the Invention
The present invention relates to a writing device for color electronic paper which is capable of performing full color display.
2. Related Art
As a non-luminous type display device, there is known an electrophoretic display device which utilizes an electrophoresis phenomenon. The electrophoresis phenomenon is a phenomenon in which, when an electric field is applied to a dispersion liquid having particulates dispersed in a liquid phase dispersion medium, particles naturally charged by the dispersion (electrophoretic particles) migrate according to a Coulomb force.
In a basic structure of the electrophoretic display device, one electrode is opposed to the other electrode at a predetermined interval, and the dispersion liquid (electrophoretic dispersion liquid) is encapsulated between the electrodes. In addition, at least one electrode is made transparent, and this transparent electrode side is set as an observation surface. When a potential difference is applied between both the electrodes, electrophoretic particles are attracted to one of the electrodes depending upon a direction of an electric field.
Consequently, if the dispersion medium is dyed with a dye and the electrophoretic particles are constituted by pigment particles in this structure, a color of the electrophoretic particles or a color of the dye can be seen from the transparent observation surface according to a direction of an electric field. Therefore, an image can be displayed by forming the electrodes in a pattern associated with respective pixels to control a voltage to be applied to respective pixel electrodes.
Such an electrophoretic display device attracts attention as an electrooptic device which is preferable for a new display because the electrophoretic display device has advantages such as a simple structure, a wide viewing angle, low power consumption, and a performance for maintaining a displayed image (a memory property).
As an example of the electrophoretic display device, there is known a microcapsule type electrophoretic display device. In this device, a layer consisting of a plurality of microcapsules containing electrophoretic dispersion liquid is arranged between electrodes opposed to each other as an electrophoretic layer.
In order to perform full color display with the microcapsule type electrophoretic display device, a layer consisting of three types of microcapsules, which are formed so as to be capable of displaying one color among predetermined three primary colors, respectively, is required as the electrophoretic layer. As an example of the microcapsule type electrophoretic display device capable of performing full color display, JP-A-2000-35598 discloses an electrophoretic display panel including a microcapsule layer in which the three types of microcapsules are arranged orderly, a pixel electrode for each microcapsule, and a common electrode which is in contact with all the microcapsules.
On the other hand, JP-A-2000-127478 discloses a microcapsule type electrophoretic display device which is divided into a display medium with a structure, which includes a microcapsule layer but does not include a drive circuit and electrodes, and a writing device having electrodes and a drive circuit. In addition, JP-A-2000-127478 describes “electronic paper”, which includes a sheet-like base material (paper) having flexibility and a microcapsule layer which is formed on the base material and has a plurality of microcapsules arranged in a planar shape and fixed by a binder therein, as the display medium.
Such electronic paper has an advantage that, while the electronic paper can perform the same high definition display as the display panel of the electrophoretic display device, it can be easily carried because it does not have a drive circuit and electrodes, and it is possible to rewrite a color image on the electronic paper with a writing device.
On the other hand, office documents have made progress in colorization through spread of color printers, and an electronic paper is required with full color display.
It will be possible to rewrite a color image with the electronic paper as a medium by dividing the microcapsule type electrophoretic display device capable of performing full color display into color electronic paper and a writing device. However, at the present point, there is no writing device which can perform rewriting with respect to the color electronic paper. It is difficult to perform writing with respect to the color electronic paper with the writing device described in JP-A-2000-127478.